As electrical contact materials such as used for connectors, switches, or printed wiring boards, there have conventionally been used a metal-plated stainless material and a surface-treated stainless steel material. The metal-plated stainless material is configured such that the surface of a stainless steel material is coated with a metal plating layer such as a gold plating layer,
In such a stainless steel material formed with a metal plating layer at the surface (referred also to as a “metal-plated stainless material,” hereinafter), underlying nickel plating may be performed to form an underlying nickel plating layer on the stainless steel material before forming the metal plating layer, in order to improve the interfacial adhesion property of the metal plating layer at the surface. In another known technique, for example, a metal plating layer may be formed directly on a stainless steel material without performing underlying nickel plating, as described in Patent Document 1. As a surface-treated stainless steel material, for example, a stainless steel material formed with a specific oxide film on the surface is known, as disclosed in Patent Document 2.